This invention relates to a carburetor, and more particularly to a rotary throttle valve carburetor for a two-cycle engine.
In a conventional rotary throttle valve carburetor a fuel-and-air mixing passage extends usually horizontally through a carburetor body providing a fuel-and-air mixture to the crankcase of a two-cycle engine. A throttle chamber communicates transversely through the fuel-and-air mixing passage and usually extends vertically through the carburetor body. A rotary throttle seats rotatably and vertically or axially movably within the chamber extending through the fuel-and-air mixing passage. The rotary throttle has a throttle bore which communicates adjustably with the fuel-and-air mixing passage. The rotary throttle extends upward from the carburetor body through a plastic lid plate engaged between the metallic carburetor body and a metallic bracket (retaining plate).
A throttle lever engaged to the upper end of the rotary throttle has a cam surface which slides over a cam follower of the bracket when the rotary throttle is rotated. During rotation, contact of the cam surface with the cam follower causes axial movement of the rotary throttle which in-effect adjusts the flow of fuel into the throttle bore. Because the bracket is supported by the plastic lid plate, age deformation of the plastic lid plate can alter the height or location of the cam follower, thereby changing the axial placement of the rotary throttle at a prescribed rotational location and altering the fuel flow.
To ensure dust and debris does not enter the throttle chamber between the throttle shaft and the plastic lid plate, a conventional rubber boot envelopes the protruding portion of the rotary throttle and throttle lever while securing about the carburetor body. The rubber boot, however, may harden with age and ultimately break off. At which point, dirt and dust can enter the throttle chamber making it difficult to rotate the rotary throttle and degrading consistent fuel flow by altering the vertical or axial placement or location of the rotary throttle within the throttle chamber.
The plastic lid plate is typical pressed against the top surface of the carburetor body via the bracket and a plurality of bolts thereby forming a seal. Should the plastic lid plate deform with age, the potential exists for dirt and dust to enter the throttle chamber between the deformed plastic lid plate and the metallic carburetor body. Even without deformation of the plastic lid plate, imperfections or scratches formed on the top or sealing surface of the carburetor body during casting or otherwise can create clearances in which dust can enter the throttle chamber.
A rotary throttle valve carburetor has a fuel-and-air mixing passage which extends through a carburetor body. A cylindrical throttle chamber extends down from a top surface of the body and communicates transversely with the fuel-and-air mixing passage. A rotary throttle seats rotatably and vertically or axially movable within the chamber and through the fuel-and-air mixing passage. The rotary throttle has a bore fully communicating and longitudinally aligned with the fuel-and-air mixing passage at wide-open throttle. The rotary throttle has a throttle shaft projecting upward through the top surface of the carburetor body and through a hole of a base portion of a plastic lid plate engaged between the top surface and a metallic bracket. An upward projecting annular shoulder of the lid plate is disposed concentrically to and spaced radially apart from the throttle shaft. A circular seal is disposed radially between the annular shoulder of the lid plate and the throttle shaft to prevent dirt from entering the valve chamber. A metallic cam follower engages the bracket and contacts a cam surface of a throttle lever engaged transversely to the upper end of the throttle shaft. The metallic cam follower or bracket is interconnected to the metallic carburetor body by a plurality of metallic spacers.
Preferably, the circular seal has a reinforcement metallic sleeve engaged to the lid plate and a baked on resilient member engaging the throttle shaft. Preferably, any clearance between the base portion of the plastic lid plate and the top surface of the carburetor body is sealed by an O-ring which seats into a circular groove defined by the top surface. Preferably, the lid plate has a lower annular shoulder which extends downward from the base portion and is press fit with a cylindrical wall of the carburetor body which extends downward from the top surface to a recessed annular shelf disposed concentrically about the throttle shaft. Preferably, the cam follower is a rotating pin projecting from a cylinder engaged to the bracket.
Objects, features, and advantages of this invention include a throttle chamber well sealed from the intrusion of dust and dirt, a reliable and friction free cam follower, and consistent fuel delivery and engine operation with age or throughout its in service useful life.
By the provision of a line contact between the cam follower and the cam surface, the surface pressure is decreased to stabilize the operating load and enhance the abrasion resistance.
The bracket is diecast to thereby enhance the strength, prevent deformation when dropped, enhance processing accuracy, and provide a partial stopper as an additional function.
There is no increase in operating load and damage of the surface due to the hardening of the resilient seal member, intrusion of dust is prevented by the resilient seal member and stability of operation of the throttle lever and flow rate of fuel are obtained without being adversely affected by the vertical movement and rotation of the rotary throttle.
A plurality of positioning bosses provided on the carburetor body eliminate deviation of the plastic lid plate and enhance assembly of the carburetor.
A clearance between the carburetor body and the plastic lid plate is sealed by an O-ring to thereby prevent intrusion of dust into the valve chamber due to the deformation of the seal surface, scratches, oil wrinkles or the like.